Decidability refers to the ability to determine, using an algorithm, whether a given problem can be solved or not. In computer science, a problem is considered decidable if there exists a procedure that can provide a yes or no answer for every possible input in a finite amount of time. An example of a decidable problem is determining whether a given number is even or odd. In contrast, some problems, like the Halting Problem proposed by Alan Turing, are undecidable, meaning no algorithm can solve them for all possible inputs.